The well-documented antiviral effects of double-stranded polyriboneucleotides in various animal model systems provided the rationale for our use of polyinosinic-polycytidylic acid (rIn.rCn) as a therapeutic agent in such patients. The overall objective is to determine whether rIn.rCn can control herpes zoster virus infection in man and to determine the role that the interferon response may play in this control. We have evaluated 35 cancer patients who were randomized to a double-blind study with zona zoster in which 18 patients received rIn.rCn and the other 17, a placebo injection. The patients were evaluated on the basis of clinical response, toxicities and antiviral responses including antibody levels and serum and vesicle fluid interferon levels. we have shown that absolute number "t" lymphocytes has a major impact on the outcome of herpes zoster infections which can "override" the effect of rIn.rCn. To date, there are no major differences in clinical outcome of herpes zoster infection whether treated with rIn.rCn or with placebo. We will also document rate-limiting toxicities of rIn.rCn: Our structure-function studies (Carter and DeClercq, 1974) might then lead to the development of a superior therapeutic agent.